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1. Investigation of Material Transport Through Triply Periodic Minimal Surface (TPMS) Bone Scaffolds Using Computational Fluid Dynamics (CFD)

   https://doi.org/10.1115/MSEC2024-123878  

   Coburn, Brandon; Salary, Roozbeh “Ross” (June 2024, American Society of Mechanical Engineers (ASME))

   Abstract Cell-laden, scaffold-based tissue engineering methods have been successfully utilized for the treatment of bone fractures and diseases, caused by factors such as trauma, tumors, congenital anomalies, and aging. In such methods, the rate of scaffold biodegradation, transport of nutrients and growth factors, as well as removal of cell metabolic wastes at the site of injury are critical fluid-dynamics factors, affecting cell proliferation and ultimately tissue regeneration. Therefore, there is a critical need to identify the underlying material transport mechanisms and factors associated with cell-seeded, scaffold-based bone tissue engineering. The overarching goal of this study is to contribute to patient-specific, clinical treatment of bone pathology. The overall objective of the work is to establish computational fluid dynamics (CFD) models to identify: (i) the consequential mechanisms behind internal and external material transport through/over porous bone scaffolds and (ii) optimal triply periodic minimal surface (TPMS) scaffold designs toward cell-laden bone fracture treatment. In this study, 10 internal-flow and 10 external-flow CFD models were established using ANSYS, correspondingly based on 10 single-unit TPMS bone scaffold designs, where the geometry of each design was parametrically created using Rhinoceros 3D software. The influence of several design parameters, such as surface representation iteration, merged toggle iso value, and wall thickness, on geometry accuracy as well as computational time, was investigated in order to obtain computationally efficient and accurate CFD models. The fluid properties (such as density and dynamic viscosity) as well as the boundary conditions (such as no-slip condition, inlet flow velocity, and pressure outlet) of the CFD models were set based on clinical/research values reported in the literature as well as according to the fundamentals of internal/external Newtonian flow modeling. Several fluid characteristics, including flow velocity, flow pressure, and wall shear stress, were analyzed to observe material transport internally through and externally over the TPMS scaffold designs. Regarding the internal flow CFD modeling, it was observed that “P.W. Hybrid” (i.e., Design #7) had the highest-pressure output, with “Neovius” (i.e., Design #1) following second to it. These two designs have a relatively flatter surface area. In addition, “Schwarz P” (i.e., Design #2) was the lowest pressure output of all 10 TPMS designs. “Neovius” and “Schwarz P” had the highest and lowest values of wall shear stress. Besides, the velocity streamlines analysis showed an increase in velocity along the curved sections of the scaffolds’ geometry. Regarding the external flow CFD modeling, it was observed that “Neovius” yielded the highest-pressure output within the inlet section, which contains the area of the highest-pressure location. Furthermore, “Diamond” (i.e., Design #8) displayed having the highest values of wall shear stress due to the results of fluid interaction that accrues with complex curved structures. Also, when we look at designs like “Schwarz G”, the depiction of turbulent motion can be seen along the internal curved sections of the structure. As the external velocity streamlines decrease within the inner channels of the designs, this will lead to an increased pressure buildup due to the intrinsic interactions between the fluid with the walls. Overall, the outcomes of this study pave the way for optimal design and fabrication of complex, bone-like tissues with desired material transport properties for cell-laden, scaffold-based treatment of bone fractures. 

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2. Numerical Design, Fabrication, and Characterization of Porous Tissue Scaffolds for Bone Regeneration

   Coburn, Brandon (July 2024, Marshall Digital Scholar (https://mds.marshall.edu/etd/1910))

   With the recent advancements within biomedical engineering of bone tissue scaffolds, there is still a need to develop mechanically robust and biocompatible with low immunogenicity for bone regeneration. Additionally, the evaluation of the fluid dynamics of the porous Triply Periodic Minimal Surfaces (TPMS) bone scaffold also shows the need for investigation due to the complex fluid interaction of hemodynamics that occurs with the scaffold internal and external domains. To aid in the development of treating bone fractures, defects, and diseases. Furthermore, with the induction of a wide variety of TPMS architecture that yields different topologies, the Convolutional Neural Network (CNN) model will aid in predicting the TPMS scaffold characteristic to help develop critical design parameters. Thus, this research has observed biocompatible and mechanically strong materials with bone regeneration applications by evaluating polyamide, polyolefin, and cellulose fibers (PAPC) and SimuBone biomaterial. The TPMS scaffolds are fabricated by fused deposition modeling (FDM) additive manufacturing. Furthermore, the evaluation of fluid dynamics of internal and external effects using the computational fluid dynamics (CFD) method is used to observe the fluid interaction of the TPMS scaffold. Therefore, ANSYS (Fluent with Fluent Meshing) software captures the pressure, wall shear stress, and velocity streamline characteristics. As for the bone scaffold topology prediction, machine learning CNN is used and developed within Python to observe these properties. Accuracy, loss, validation accuracy, validation loss, and F-Score will be recorded to aid in developing the hyperparameters with the CNN platform. Therefore, the findings show that PAPC compression modulus performance observed that Neovius and Schwarz-Diamond designs have higher levels of compression strength than that of Schwarz-Primitive and Schwarz-Gyroid designs. As for SimuBone biomaterial, it was observed to be a suitable bone tissue engineering material due to its robust mechanical performance. Additionally, it is observed that the vertical orientations of P.W. Hybrid showed optimal performance with the compression analysis out of 10 different TPMS designs. It also has suitable mechanical mimicry of human trabecular bone yield strength. The evaluation of the CFD analysis of the internal and external performance of 10 TPMS scaffold designs showed that Schwarz Primitive yielded superior fluid properties. The wall shear stress was the lowest for analysis, with the external cubic evaluation showing Schwarz Primitive has a wall shear stress value of 3.4 mPa. In addition, its fluid pressure performance was suitable for improving cell viability and survival. Furthermore, the CNN evaluations displayed the optima hyperparameter for batch size, convolutional layers, dense layers, layer size, and Epoch training as 16, 6, 3, 32, and 25, respectively. A trend can be discerned within accuracy, loss, validation accuracy, validation loss, and F-Score performance, all yielding improved and consistent performance with the 5-replication analysis. Thus, this research has observed the fluid dynamics, mechanical performance, and topology evaluation of the TPMS bone scaffold. This study will aid in designing and experimenting with bone tissue engineering scaffold development. 

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3. Mechanical Characterization of Porous Bone-like Scaffolds with Complex Microstructures for Bone Regeneration

   https://doi.org/10.3390/bioengineering12040416  

   Coburn, Brandon; Salary, Roozbeh Ross (April 2025, Bioengineering)

   Janorkar, Amol V; Vozzi, Giovanni (Ed.)

   The patient-specific treatment of bone fractures using porous osteoconductive scaffolds has faced significant clinical challenges due to insufficient mechanical strength and bioactivity. These properties are essential for osteogenesis, bone bridging, and bone regeneration. Therefore, it is crucial to develop and characterize biocompatible, biodegradable, and mechanically robust scaffolds for effective bone regeneration. The objective of this study is to systematically investigate the mechanical performance of SimuBone, a medical-grade biocompatible and biodegradable material, using 10 distinct triply periodic minimal surface (TPMS) designs with various internal structures. To assess the material’s tensile properties, tensile structures based on ASTM D638-14 (Design IV) were fabricated, while standard torsion structures were designed and fabricated to evaluate torsional properties. Additionally, this work examined the compressive properties of the 10 TPMS scaffold designs, parametrically designed in the Rhinoceros 3D environment and subsequently fabricated using fused deposition modeling (FDM) additive manufacturing. The FDM fabrication process utilized a microcapillary nozzle (heated to 240 °C) with a diameter of 400 µm and a print speed of 10 mm/s, depositing material on a heated surface maintained at 60 °C. It was observed that SimuBone had a shear modulus of 714.79 ± 11.97 MPa as well as an average yield strength of 44 ± 1.31 MPa. Scaffolds fabricated with horizontal material deposition exhibited the highest tensile modulus (5404.20 ± 192.30 MPa), making them ideal for load-bearing applications. Also, scaffolds with large voids required thicker walls to prevent collapse. The P.W. Hybrid scaffold design demonstrated high vertical stiffness but moderate horizontal stiffness, indicating anisotropic mechanical behavior. The Neovius scaffold design balanced mechanical stiffness and porosity, making it a promising candidate for bone tissue engineering. Overall, the outcomes of this study pave the way for the design and fabrication of scaffolds with optimal properties for the treatment of bone fractures. 

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4. A Computational Fluid Dynamics Model for Investigation of Material Flow in a Perfusion Bioreactor Toward Optimal Biomedical Design of Cell-Laden Scaffolds for Bone Regeneration

   https://doi.org/10.1115/IMECE2024-139666  

   Rollins, Hannah; Salary, Roozbeh “Ross” (November 2024, American Society of Mechanical Engineers (ASME) - International Mechanical Engineering Congress and Exposition (IMECE 2024))

   Abstract In tissue engineering, once a scaffold has completed mechanical property testing, it must then undergo biological characterization which determines if the scaffold is capable of supporting cell viability. To perform biological tests, cells must be seeded onto a scaffold with the help of bioreactors, the four main types being: (i) rotating wall, (ii) spinner flask, (iii) compression, and (iv) perfusion bioreactor. In perfusion bioreactors, a consistent flow of material is introduced (using a pump) into the inlet of the bioreactor chamber where multiple scaffolds of a disc geometry are located. However, the intrinsic, complex interaction between the scaffolds and material flow as it goes through the bioreactor chamber affects the viability of the seeded stem cells. Therefore, there is a need to identify consequential fluid dynamics phenomena governing the material flow in a perfusion bioreactor. In this study, using a CFD model, the effects of critical scaffold parameters (such as the number of scaffolds, scaffold diameter, scaffold thickness, and number of pores) on the main flow properties (i.e., flow pressure, wall shear stress, and streamline velocity) influential in cell proliferation and bone development will be investigated. It was observed that increasing the number of pores, in addition to decreasing the pore diameter had an adverse effect on the maximum forces occurring on the scaffold. In addition, changing the overall scaffold diameter did not appear to have as much as an effect as the other parameters. Furthermore, it was observed that a decrease in porosity would lead to an increase in wall shear stress and consequently in cell death. Overall, the outcomes of this study pave the way for optimal design, fabrication, and preparation of cell-laden bone scaffolds for treatment of bone fractures in clinical settings. 

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5. A Simulation Approach to Determine Internal Architecture of 3D Bio-Printed Scaffold Suitable for A Perfusion Bioreactor

   Clark, S.; Quigley, C.; Mankowsky, J.; & Habib, M. A. (May 2023, Proceedings of the IISE Annual Conference & Expo 2023)

   Babski-Reeves, K; Eksioglu, B; Hampton, D. (Ed.)

   Traditional static cell culture methods don't guarantee access to medium inside areas or through the scaffolds because of the complex three-dimensional nature of the 3D bio-printed scaffolds. The bioreactor provides the necessary growth medium encapsulated and seeded cells in 3D bioprinted scaffolds. The constant flow of new growing medium could promote more viable and multiplying cells. Therefore, we created a specialized perfusion bioreactor that dynamically supplies the growth medium to the cells implanted or encapsulated in the scaffolds. A redesigned configuration of our developed bioreactor may enhance the in vivo stimuli and circumstances, ultimately improving the effectiveness of tissue regeneration. This study investigated how different scaffold pore shapes and porosities affect the flow. We employed a simulation technique to calculate fluid flow turbulence across several pore geometries, including uniform triangular, square, circular, and honeycomb. We constructed a scaffold with changing pore diameters to examine the fluid movement while maintaining constant porosity. The impact of fluid flow was then determined by simulating and mimicking the architecture of bone tissue. The best scaffold designs were chosen based on the findings. 

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